1. Field of the Invention
This invention relates to methods and apparatus for the continuous inspection and control of objects which are made of transparent substance, such as glass, in order to eliminate those objects which are defective. More particularly it relates to the inspection of objects such as the mouths of bottles and flasks, which have at least a localized region with symmetry of revolution.
2. Nature and History of the Art
Because of their configuration and the function which they perform, the mouths of glassware vessels often represent a critical region on which the quality of the glassware depends.
One defect that is commonly encountered at the abovementioned region is an internal flaw, referred to as a "glaze", which is likely to cause the glass to break or, at times, to produce an unsatisfactory seal. This defect gives rise to a reflecting surface which most often lies within a radially-oriented vertical plane or within a nearly horizontal plane. It is primarily located at points of variation of cross-section. Another defect which is also encountered is chipping, which affects the evenness of the drinking rim and is responsible for corking or stoppering defects.
The prior art provides for a photo-optic examination of hollow glassware for the purpose of detecting possible glazes. This examination is typically carried out by means of circular scanning which makes use of light beams that illuminate, locally, the neck, rim or other portions of the glassware. The light reflected by a glaze is detected by receivers which control an ejecting device designed to remove the defective items automatically from the conveyor belt.
In order to increase the sensitivity without increasing background noise or other parasitic signals, use is preferably made of a different combination of optical members arranged in a manner appropriate for detecting each given type of defect, i.e. an emitting unit which generates one or more narrow light beams is associated with one or more detecting cells.
It is of value to combine several monitoring devices in the same station wherever possible, but such combination of prior art devices requires careful separation of the different signals, either geometrically or electronically, based on different modulations.
Finally, the apparatus provided by the prior art affords the possibility of presetting, but the adaptation of this apparatus to each particular defect continues to pose a difficult problem. Thus, while such apparatus has been generally satisfactory, it has, nevertheless, been plagued by certain drawbacks and limitations.
One prior art approach involves momentary stopping or slowing down each glassware item and rotating it in order to carry out a complete examination. Apparatus using this approach typically includes a transfer device designed to bring the item from a rectilinear horizontal conveyor belt to a control station. This transfer device is typically highly complex, and its mechanism does not permit the conveying of more than 400 to 500 glassware items per minute. This method is particularly difficult to apply to those glassware items which are noncylindrical in shape, and it undesirably entails an additional handling of the fragile glass object. While this approach can be used at production-line outlets, it is not generally suitable for high speed production lines such as bottling operations.
A second approach involves examining each object with a rotating inspection head as the moving object passes under the control station, without shutting down the conveyor belt or handling or rotating the object. This approach calls for a very high speed rotation head, the speed of which may range within 15,000 to 20,000 revolutions per minute. The head is generally equipped with several associated transmitter-receiver pairs which are precisely oriented with respect to one another so as to delimit different inspection areas or to detect different defects. Nonetheless, the number of examinations made per unit of time remains relatively limited because the apparatus will not operate on objects that are moved too rapidly by the conveyor belt.